The retention sites and residence times for inhaled particles deposited in the non-ciliated pulmonary regions are important factors in the pathogenesis of major occupational respiratory diseases, i.e., silicosis, coal workers pneumoconiosis (CWP), asbestosis, and in cancer associated with inhaled mineral fibers. This study is directed toward the quantitative characterization of the transport rates and storage sites for respirable particles of coal, granite, ferric oxide, tantalum and glass; with defined size, shape and concentration, and for short and long mineral fibers. Particle retention within the thorax and tracheal lymph nodes following a single brief aerosol inhalation will be measured in 150 rabbits and 4 donkeys by the external in-vivo detection of radionuclides within the particles. In addition, the retention of ferromagnetic particles will be measured by remanent magnetism. For 8 groups of 15 rabbits each, an 8 month control test involving in-vitro retention measurements of inert tagged particles deposited by inhalation will precede an exposure to a particular aerosol of interest. The initial tests will provide a basis for estimating population variability and provide a baseline for each individual animal for comparison with the subsequent serial sacrifice experiments on the same animals. Particle translocations will be characterized for the serial sacrifice tests in terms of tissue burdens, the degree of particle ingestion by alveolar macrophages, and by autoradiography to establish the rate of particle accumulation in dust foci. One lung from each rabbit will be preserved for a coordinate histological evaluation which will determine the proportions within the various cell types and the extracellular depots. The effect of low dose and high dose cigarette smoke exposure on alveolar particle clearance will be determined in tests on donkeys.